The invention relates to a lens barrel, and more particularly, to a lens barrel which may be mounted on a single lens reflex camera to allow a taking lens to be driven by a motor for the purpose of distance adjustment.
In an arrangement of the type described, the motor used is normally driven at a high rate in order to achieve a rapid distance adjustment. If the taking lens is driven at a high speed when moving toward its extreme positions, either toward the infinity or the nearest point, it is impossible to allow the taking lens to be stopped smoothly at such extreme position. Each time the lens is stopped at such position, it abuts against a stop to produce an offensive percussion sound and also applies an impact to the lens system. It is highly desirable to eliminate such difficulty by changing the drive applied to the lens to a lower rate immediately before an extreme position is approached. It will also be very useful to a user if a choice between a rough movement of the lens through a relatively large stroke and a fine movement of the lens through a limited stroke is enabled in a simple manner even in a region remote from the vicinity of the extreme positions.
A lens barrel is also known having an "auto-focus" function which allows a taking lens to be driven to an in-focus position in response to a signal representing the result of a distance measurement. If an object being photographed moves too rapidly, the movement of the lens fails to follow such movement of the object, disabling a focussing operation of the taking lens. Accordingly, it is desirable in such instance that a user be enabled to recognize this fact immediately. In an "auto-focus" lens employing a focussing sensor of TTL (through-the-taking lens) type, a parallax as experienced in the triangulation is avoided, and a distance measurement up to a very near point is enabled. However, it is also desirable that a user be allowed to recognize, as soon as possible, that an object being photographed is located at a distance which is less than that which lies within the reach of the focussing operation and hence the taking lens can no longer be controlled.
The recent trend is toward a multi-mode capability of the lens barrel, and hence it is desirable that the lens barrel be provided with as many functions as possible while substantially simplifying the operation and appearance thereof.